lucene 例子
在Lucene中，权重计算是由 Similarity 类及其子类负责的。
以下是一个简单的Java示例，演示如何使用Lucene的TFIDFSimilarity来计算文档的权重。
请注意，以下示例使用Lucene的版本为8.x。
具体实现可能会根据Lucene版本而有所不同。
首先，你需要添加Lucene的依赖：
<!-- Add Lucene dependencies to your project -->
<dependency>
<groupId>org.apache.lucene</groupId>
<artifactId>lucene-core</artifactId>
<version>8.11.1</version> <!-- Replace with the latest version -->
</dependency>
<dependency>
<groupId>org.apache.lucene</groupId>
<artifactId>lucene-analyzers-common</artifactId>
<version>8.11.1</version> <!-- Replace with the latest version -->
</dependency>
然后，以下是一个简单的Java示例，演示如何使用Lucene的TFIDFSimilarity计算文档的权重：
import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.standard.StandardAnalyzer;
import org.apache.lucene.document.Document;
import org.apache.lucene.document.Field;
import org.apache.lucene.index.IndexWriter;
import org.apache.lucene.index.IndexWriterConfig;
import org.apache.lucene.index.IndexWriterConfig.OpenMode;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.Query;
import org.apache.lucene.search.ScoreDoc;
import org.apache.lucene.search.TermQuery;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.RAMDirectory;
import org.apache.lucene.util.Version;
import org.apache.lucene.search.similarities.TFIDFSimilarity;
public class LuceneTFIDFExample {
public static void main(String[] args) throws Exception {
// 创建内存索引目录
Directory indexDirectory = new RAMDirectory();
// 使用标准分词器
Analyzer analyzer = new StandardAnalyzer();
// 配置IndexWriter
IndexWriterConfig config = new IndexWriterConfig(analyzer);
config.setOpenMode(OpenMode.CREATE_OR_APPEND);
// 创建IndexWriter
IndexWriter indexWriter = new IndexWriter(indexDirectory, config);
// 添加文档到索引
addDocument(indexWriter, "1", "Lucene is a full-text search library.");
addDocument(indexWriter, "2", "It is widely used for information retrieval.");
// 提交事务
indexWriter.commit();
// 使用相似度模型 TFIDFSimilarity
TFIDFSimilarity similarity = new TFIDFSimilarity();
// 创建IndexSearcher
IndexSearcher indexSearcher = new IndexSearcher(indexWriter.getReader());
indexSearcher.setSimilarity(similarity);
// 查询
Query query = new TermQuery(new org.apache.lucene.index.Term("content", "search"));
ScoreDoc[] hits = indexSearcher.search(query, 10).scoreDocs;
// 输出查询结果
for (ScoreDoc hit : hits) {
Document hitDoc = indexSearcher.doc(hit.doc);
System.out.println("Document ID: " + hitDoc.get("id") + ", Score: " + hit.score);
}
// 关闭IndexWriter
indexWriter.close();
}
private static void addDocument(IndexWriter indexWriter, String id, String content) throws Exception {
Document document = new Document();
document.add(new Field("id", id, Field.Store.YES, Field.Index.NO));
document.add(new Field("content", content, Field.Store.YES, Field.Index.ANALYZED));
indexWriter.addDocument(document);
}
}
在此示例中，我们使用了 TFIDFSimilarity 作为相似度模型，并使用标准分词器。
addDocument 方法用于向索引中添加文档。
在查询时，我们使用 TermQuery 查询，并输出文档的得分。请注意，得分的具体计算取决于所选的相似度模型。
这只是一个简单的示例，实际应用中可能需要更多的配置和处理。
在实际项目中，你可能需要更复杂的分析器、索引字段、相似度模型等，以满足具体需求。
核心类
我们根据这个入门例子，可以找到对应的核心类：
Directory 内存索引目录 Analyzer analyzer 使用标准分词器 IndexWriter indexWriter 创建IndexWriter Document 文档
IndexSearcher 查询类 ScoreDoc 分数结果 Query 查询
Directory 类
源码
public abstract class Directory implements Closeable {
public abstract String[] listAll() throws IOException;
public abstract void deleteFile(String name) throws IOException;
public abstract long fileLength(String name) throws IOException;
public abstract IndexOutput createOutput(String name, IOContext context) throws IOException;
public abstract IndexOutput createTempOutput(String prefix, String suffix, IOContext context)
throws IOException;
public abstract void sync(Collection<String> names) throws IOException;
public abstract void syncMetaData() throws IOException;
public abstract void rename(String source, String dest) throws IOException;
public abstract IndexInput openInput(String name, IOContext context) throws IOException;
public ChecksumIndexInput openChecksumInput(String name) throws IOException {
return new BufferedChecksumIndexInput(openInput(name, IOContext.READONCE));
}
public abstract Lock obtainLock(String name) throws IOException;
public abstract void close() throws IOException;
protected void ensureOpen() throws AlreadyClosedException {}
public abstract Set<String> getPendingDeletions() throws IOException;
}
IndexWriter
IndexReader
IndexSearch
Analyzer
Query
Document
ScoreDoc
public class ScoreDoc {
/** The score of this document for the query. */
public float score;
/**
* A hit document's number.
*
* @see StoredFields#document(int)
*/
public int doc;
/** Only set by {@link TopDocs#merge} */
public int shardIndex;
//
}
